Increasing EGC for Voltage Drop

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bphgravity

Senior Member
Location
Florida
250.122(B) requires that the EGC to be increased proportionately according to circular mil area of the increase of the ungrounded conductors. Generally, EGC are sized per Table 250.122 in accordance to the OCD. When an increase in ungrounded conductors are made due to voltage drop corrections, you don't increase the OCD to match the conductor. So what would be the reason to have to increase the EGC if the rating of the OCD doesn't change? I understand that ground faults in the larger conductors will produce higher fault currents back on the EGC, but so much to need a larger EGC?
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: Increasing EGC for Voltage Drop

Not sure why the NEC made the requirement but here is what I think. If you are increasing the conductor size to overcome voltage drop, then the distances are long resulting in higher circuit impedance. The EGC is increased proportionally to overcome the higher impedance of the longer distances encountered to ensure proper OCPD operation.
 

Nick

Senior Member
Re: Increasing EGC for Voltage Drop

Dereckbc,
Exactly correct. If there is enough voltage drop in the ungrounded conductors to require larger conductors there will be enough drop during a fault to limit the ability of the OC device to open.
 
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